Over a light lunch of lobster and prosciutto croquettes and a small sauvignon blanc at J Sheekey’s, the clinical negligence silk whose biography of eminent Victorian barrister Sir Edward Marshall Hall is out this month, consider what makes a great advocate, the stress of taking capital cases and the changing legal times.

Sally Smith QC established a medical law practice at London’s One Crown Office and has worked on some of the most high-profile cases, including the Alder Hey hospital child organ retention case, leading the prosecution of the doctor who sought to draw a link between autism and MMR and representing the strategic health authority in the Mid Staffs public inquiry.

And she met her cardiologist husband, Professor Roger Hall, who was her expert witness during a long-running clinical negligence case.

But she fell into law by accident, in the first term of a history degree at the LSE under the tutorship of the, then unknown, David Starkey. ‘I went to a lecture thinking it was going to be on the Tudors, but it turned out to be on the law of contract. I felt too shy to clamber out over all of these denim-clad knees, so I sat it out.’

Finding that law floated her boat more than history, Smith told Starkey that she wanted to swap subjects. ‘He said: “It’s entirely up to you, but you’ll be terribly, terribly bored”’.

Smith has always been passionate about biographies. ‘I don’t care who they’re about. I’ve always had this preoccupation with the nature of truth,’ she says, apologising for sounding ‘terribly pompous’.

‘It ties in very well with being a lawyer. I’m interested in versions of events and have leant there’s no such thing as truth’.

Pointing out that law and biography are about looking at evidence, she says: ‘This sounds really nerdy, but if I read a biography or a diary, where the subject has been to a dinner party, I’ll go and look up somebody else who was at it and read their account of the same dinner party.’

For years, she says, she had fancied penning one herself, but struggled to find an appropriate subject. She read the first biography of Marshall Hall, written by barrister and Tory politician Edward Marjoribanks and wanted to find out more about the man behind the myth, from a modern perspective.

‘Because it was written in 1929 it’s very restrained about his personal life and quite uncritical. I thought it would be interesting to see what he was really about. I began some Googling and it sort of turned into a project’.

Her internet sleuthing turned up an auction house selling artefacts that had belonged to him, including a desk and smoking jacket. Pursuing the trail, she wrote asking the auction house to pass her details on to the seller.

‘Two weeks later the phone rang and it was a lady in Wales. Her father had been Marshall Hall’s daughter’s executor. Marshall Hall’s daughter had never married and left everything in her house to this woman’s father’.

The lady had boxes and boxes of his papers, which had been gathering dust in her loft for years. Smith drove down to have a read and was then on a roll. From the papers, she found a close friend of his at the bar and contacted his family.

He had prosecuted Marshal Hall on many occasions and his family had kept a lot of the briefs. ‘I was literally undoing the pink ribbon on briefs which hadn’t been undone for a hundred years. It was extraordinary’.

Marshall Hall was involved in some of the most famous trials of his age, including the Camden Town murder, Seddon the Poisoner, the Brides in the Bath, the Green Bicycle Murder and the Murder at the Savoy.

Finding out about them, did not require much detective work. ‘He was the most consummate self-publicist you could possibly imagine and kept every press cutting from his first case, when he was totally unknown. They’re all in Inner Temple library – 38 volumes.’

Hall, born in 1858 and died during a trial in 1927, notes Smith, saved more people from the hangman’s noose than any other barrister. A combination of his moving and passionate oratory, charm and good looks saw him achieve a level of fame that no other barrister has, or will.

‘He was absolutely adored by the public, who felt that he was a saviour of the common man. He was a film star figure and showman. The newspaper headlines called him the handsomest man in England.’

‘When he died, the King sent a telegram to his wife, all the shops along the funeral route closed, cars and buses stopped and the working men in the street doffed their caps and stood in reverence as the cortege drove passed’.

Explaining the secret of his success, she observes: ‘He was six foot three, when the average height was five foot eight. He was said to be impossibly charming and he was famous for having the most beautiful voice.

‘This may not be what people like to hear, but if you’re a man being very tall and, whatever sex you are, being exceptionally good looking, is inevitably going to help’.

She adds: ‘He had the raw material – a mixture of real emotion and technique. In the end, you’ve just got it or you haven’t, even now. You can train anyone up to a point, but the extra bit that makes someone exceptional is innate’.

Advocacy then, says Smith, involved a lot of theatrical technique and would seem ‘ridiculously over-dramatic’ nowadays, but it determined the outcome of cases more so than today because people were tried on so little evidence.

‘Forensic evidence was at an embryonic stage. It wasn’t until 1901 that they were able to distinguish human blood from animal blood, finger-printing evidence was not used until 1903 and there was no court of appeal until 1907.’

‘People were hanged pretty soon after being convicted. I don’t think we realise what an extraordinary pressure that was on the bar. To have a healthy man whose entire fate was resting on what you happened to say on a particular day, is a very odd thought’.

Marshall Hall, says Smith, was haunted by the people that he did not get acquitted and he would write to them afterwards saying ‘may God have mercy on your soul’.

His private life, she notes, was just as sensational as his public life – with two turbulent marriages and mistresses.

‘He married his childhood sweetheart with whom he had a terribly miserable marriage from the word go’. Teasingly, she says: ‘You’ll have to read the book to find out why’.

But she does give away that it ended in tragedy after she had an affair with a French officer in the Indian army. ‘He sent her off for an illegal abortion in the most sordid of circumstances and she died after the most dreadful botch-up. The abortionist was charged with her murder and tried at the Old Bailey while Marshal Hall was a very young barrister’.

After her death, says Smith, Marshall Hall ‘went into complete decline and was desperate with unhappiness for years’. But the experience, she says, made him acutely aware of the suffering of women and he became famous for championing women throughout his career.

‘In the day when prostitutes were regarded as absolutely disposable and judges described them as brazen and wanton, Marshall Hall stood up in front of an all male juries and said these women were what men had made them’.

She quotes the line from the speech that made him famous: ‘As a prostitute sat in the dock weeping, he said: “look at her members of the jury – God never gave her a chance, won’t you?”’

Former barrister and broadcaster, Clive Anderson, wrote the foreword to the book. ‘He said that Marshall Hall had emotional intelligence. I think that’s true, and that’s why people loved him,’ says Smith, who admits to wishing that she had made the observation herself.

Having recently become engrossed in The Archer’s storyline of Helen who, after a slow burn of emotional abuse, snapped and stabbed her controlling, manipulative husband Rob, Smith is sure Marshall Hall would have been fighting Helen’s corner. ‘I’m sure he would have done it beautifully’.

She is equally as confident that he would not have had much time for the dreaded Quality Assurance Scheme for Advocates (QASA). ‘One of the things Marshall Hall was famous for was being indescribably offensive to judges. So I don’t think he’d think much of the idea of being assessed by judges. I think he’d treat it with contempt’.

Marshall Hall, says Smith, paid the price for his contempt of the establishment. ‘He was never made a High Court judge, and people have always questioned why’.

Smith thinks she has unearthed the reason – contained in a handwritten footnote in parliamentary archives. But she is giving nothing away. ‘You’ll have to read the book to find out.’

Having got her first book under her belt, Smith is keen to write another. She is not going back to practice, but will remain an associate member of her chambers, while she works on it. ‘I feel really in need of a change and I’d like to try to reinvent myself before it’s too late and I just retire’.

The next biography will be another legal personality – someone who is ‘interesting and also dead’.

‘My perfect period is the Marshall Hall period. He spanned the late Victorian and early Edwardian era, which was the beginning of a system of recognisable English law.

‘The law courts in The Strand were built, a new way of administering justice came in, with daily cause lists and things that made the public aware of what was going on. The Bailey was built in 1907,’ she says.

The period, she says, is not too distant in time that she cannot envisage it, but distant enough to be romantic.

She regrets the loss of the former romance of the Inns of Court, but points out that she, as a woman, would not have been admitted to the bar at that time.

‘It wasn’t until the First World War that women could come to the bar. When women first served on juries, they had a special room with mirrors and hairpins, and an article in The Times questioned how they would be able to do their public duty and still be able to perform their domestic duties.’

On balance, she concludes: ‘I think we should be glad of the changes that have taken place since then’.

Marshall Hall: A Law unto Himself is published by Wildy & Sons.